Rotary drill bits are frequently used to drill oil and gas wells, geothermal wells and water wells. Rotary drill bits may be generally classified as rotary cone or roller cone drill bits. Fixed cutter drilling equipment or drag bits may also be used. Fixed cutter drill bits or drag bits are often formed with a matrix bit body having cutting elements or inserts disposed at select locations of exterior portions of the matrix bit body. Fluid flow passageways are typically formed in the matrix bit body to allow communication of drilling fluids from associated surface drilling equipment through a drill string or drill pipe attached to the matrix bit body. Such fixed cutter drill bits or drag bits may sometimes be referred to as “matrix drill bits.”
Matrix drill bits are typically formed by placing loose matrix material (sometimes referred to as “matrix powder”) into a mold and infiltrating the matrix material with a binder such as a copper alloy. Infiltration is a process by which melted binder material flows by capillary action through the matrix material. During infiltration, the binder material is melted and the matrix material is not melted. Typically, infiltration may be conducted at temperatures lower than would be required for sintering because sintering requires that the matrix material also be at least nearly melted. Thus, because the melting temperature of binder material is lower than the melting temperature of matrix material, infiltration may be performed at a relatively lower temperature than sintering.
In some prior art drill bits, one or more components of a bit body (e.g., bits, teeth, cutters, and inserts) have been formed and/or joined by sintering, requiring very high temperature and very high pressure. For example, the term “cemented carbide” is often used to refer to a material made by cementing tungsten monocarbide (WC) grains in a binder matrix of cobalt metal by liquid phase sintering. Sintering may require expensive and large equipment. In addition, the high temperatures required may induce chemical changes and/or physical changes in the materials used to form the components.
A process called “hot pressing” has also been used form and/or join components, wherein the components are subjected to high pressure and a relatively lower temperature than required for sintering at atmospheric pressure. Because the component is subjected to high pressure, it may be formed at a relatively lower temperature.
Infiltration molds may be formed by milling a block of material such as graphite to define a mold cavity with features that correspond generally with desired exterior features of the resulting matrix drill bit. Various features of the resulting matrix drill bit such as blades, cutter pockets, and/or fluid flow passageways may be provided by shaping the mold cavity and/or by positioning temporary displacement material within interior portions of the mold cavity. A preformed steel shank or bit blank may be placed within the mold cavity to provide reinforcement for the matrix bit body and to allow attachment of the resulting matrix drill bit with a drill string.
In infiltration process, a quantity of matrix material typically in powder form may then be placed within the mold cavity. The matrix material may be infiltrated with a molten metal alloy or binder which will form a matrix bit body after solidification of the binder with the matrix material. Tungsten carbide powder is often used to form conventional matrix bit bodies and copper is used as the binder material.